This invention relates to seismic exploration for oil and gas, and more particularly to a method for processing and displaying seismic data obtained along a seismic line of exploration.
In seismic exploration, acoustic energy is imparted into the earth at a plurality of acoustic energy generating positions (i.e. shot points) along a desired line of exploration. Such acoustic energy is reflected at interfaces between rock layers of varying acoustic impedance. Its return to the surface of the earth can be detected by seismic receivers, commonly referred to as geophones when used in land exploration and as hydrophones when used in marine exploration. The recorded output of such a seismic receiver is referred to as a seismic trace. When the trace is recorded in analog form on a magnetic tape, there is a continuous record written on the tape of an output voltage of a seismic amplifier used in conjunction with the recording of the electrical signals generated by the seismic receivers. When processed in analog form, these electrical signals are operated upon, for example, by filtering, to present them in form for use by geophysicists. With the advent of digital recording of seismic data, a discontinuous record of the signal is written that measures the seismic amplifier output voltage only at discrete intervals. The digitally recorded data may be operated upon to present the data in form for use by geophysicists. The recording of the seismic energy is commonly displayed as a seismogram having a plurality of traces printed side by side thereon and having a means superimposed thereon for timing the recorded events. The recorded event of energy reflected from a reflecting interface, hereafter referred to as from a subsurface formation, is a relatively high amplitude wavelet peak, commonly referred to as a reflection. If the plurality of traces are corrected for the differing source-to-receiver distance, the reflection peaks from a common subsurface interface will line up across the seismogram.
It is also well known that as seismic detectors become displaced further and further from the shot points for the source of seismic energy, the relative amplitudes of the seismic reflections drop off due to divergence of the generally spherical wave front as it travels through the subsurface formation. It is known to apply automatic gain control (AGC) to the weaker reflections of a given trace so that the average amplitude of the trace is more close to constant, so as to enable more efficient analysis of the seismogram.